1. Field of the Invention
The present invention relates to a valve timing controller, and more particularly to a valve timing controller for varying open/close timing of a valve in an internal combustion engine depending on the driving state.
2. Description of Related Art
In the art of automobile, it is generally known, for example, from Japanese Patent Laid Open Publications 59-115413 and 5-33615 that open/close timing of an intake valve is varied (for valve timing advance and valve timing retardation) depending on the driving state, namely, the engine speed and the engine torque.
In such a conventional valve timing controller, a rotating force is transmitted from a crank shaft to a cam shaft for driving an intake valve via a helical gear, and a hydraulic piston is provided on the cam shaft at an end. The hydraulic piston has hydraulic chambers at both sides, and hydraulic oil is supplied to selectively either of the hydraulic chambers. The piston moves the helical gear in a direction along the axis of the cam shaft, and the engaging position of the helical gear is changed along the array of teeth. Thereby, the rotating phase of the cam shaft with respect to the crank shaft is advanced or retarded.
However, because two hydraulic chambers are provided in the axial direction of the cam shaft and because the piston and the helical gear are moved in the axial direction, the conventional valve timing controller requires a large space in the axial direction and becomes large and heavy. Further, since the rotating phase is varied by the movement of the helical gear, the responsiveness in changing the rotating phase is a problem.